Regards, Jason H.
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"The existence of extraterrestrials is not an issue that can be determined on the basis of theory, no matter how compelling the arguments. SETI by definition is an experimental science." - Frank Drake

The most reasonable explanation is that we have not crossed paths within historical memory due to the geometries of scale of the universe.

There are two other options which are less likely, but possible. The first is that there is no (or very little) extra-terrestrial sentience in the universe. The second is that they are here or have been here or both and for altruistic reasons (i.e. anonymous helpfulness) choose not to make themselves detectable.

These, and other very interesting and informative options have been discussed in the thread The Silence is Deafening.

maybe we are the first life forms to achieve this state of being and tech. Maybe they have observed the way we handled finding new lands/people in our past or our tendency towards violence and decided it's not worth the risk.

all the others require a huge amount of speculation on science we don't understand yet (and won't for some time) and anthropomorphize(ing) of aliens and some stolen plots from sci-fi.

BIG universe, puny humans..

The problem with this thinking is in our hubris we think we are the end of evolution instead of just another step.

Scale is dependent on TWO things: Lifespan and distance. Two planets 500 light years apart is beyond humans ability to travel at practical velocities. However these same velocities and the trip itself my be trivial to a lifeform that can live 100,000 years.

Or, to put another way, to a fly that lives one day a journey to the end of the block takes a lifetime yet to us humans it is merely a short jaunt.